Nulling interferometer brings areas near stars into view
Planets orbiting other stars are impossible to see with standard methods because the planets are too small, faint, and close to their stars. In the 1970s, Ronald Bracewell of Stanford University (Palo Alto, CA) suggested looking in the infrared, where planets are relatively brighter, and using interferometry to neutralize starlight. The idea was thought impractical at the time, but now a team from the University of Arizona (Tucson, AZ) and the Harvard-Smithsonian Center for Astrophysics (Cambridge, MA) have demonstrated that a nulling interferometer can work.
Two 4.5-m telescopes 5 m apart observing at a wavelength of 10 µm imaged the star Betelgeuse. With a single-pass beamsplitter, the wavefronts were superimposed until they canceled each other, except for flickering caused by atmospheric turbulence. Astronomers were able to see light from as close as 0.2 arcsec to the star. They saw directly, for the first time, a dust nebula surrounding Betelgeuse that had been deduced from spectral analysis. With adaptive optics, researchers say, ground-based telescopes using Bracewell interferometry should be able to find warm, Jupiter-sized planets up to 10 parsec from Earth and analyze them spectroscopically. It may require a space-based system to find an Earth-sized planet.
